With one suspect in custody, a city mourns the victims and investigators seek answers.

Caption

With one suspect in custody, a city mourns the victims and investigators seek answers.

April 25, 2013 Aaron Hern of Martinez, Calif., looks up at his mother, Katherine, and father, Alan, as they visit the area of the second bombing at the Boston Marathon finish line on Boylston Street in Boston's Copley Square. Hern, 11, was injured during the second bombing on April 15.Elise Amendola/AP

Authorities pressed forward Saturday in their search for answers in the Boston Marathon bombing, and the person who likely knows more than anyone else is the surviving suspect, Dzhokhar Tsarnaev, 19, known to friends as “Jahar.” He remained hospitalized with gunshot wounds and was “not able to communicate yet,” said Massachusetts Gov. Deval L. Patrick.

Tsarnaev is at heavily guarded Beth Israel Deaconess Medical Center, the same hospital where his older brother, Tamerlan, 26, was pronounced dead Friday after a shootout with police in the Boston suburb of Watertown.

“One of the reasons why I and so many others are hoping the suspect survives is we have a million questions we want to ask him,” the governor said in an interview. “He’s in serious but stable condition. He’s in bad shape. He was bleeding for nearly a day. He was pretty weak and not in great shape.”

If and when he recovers, Tsarnaev is expected to be questioned by a special federal team of interrogators from the CIA, FBI and the military, tasked with grilling high-value terrorism suspects. The marathon bombing, which killed three people and wounded more than 170, has not been linked so far to any overseas terrorist network or any larger terrorist cell within the United States.

The brothers are also believed by authorities to be responsible for the shooting death of a Massachusetts Institute of Technology police officer, 26-year-old Sean Collier, on the school’s campus late Thursday night.

See the full sequence of events in the aftermath of the Boston Marathon bombings.

Federal prosecutors are planning to bring charges against the surviving suspect, but the complaint had not been filed as of late Saturday afternoon.

Authorities have not read him his Miranda rights, which include the right to remain silent and the right to an attorney. Federal law enforcement officials said they plan to use a public safety exception, outlined in a 1984 Supreme Court decision, “in order to question the suspect extensively about other potential explosive devices or accomplices and to gain critical intelligence.”

A delay in issuing Miranda warnings is justified when suspected terrorists are captured in the United States, according to a 2010 memorandum from the Justice Department. But on Saturday, the American Civil Liberties Union warned against too broad of an interpretation of that public safety exception.

“Every criminal defendant is entitled to be read Miranda rights. The public safety exception should be read narrowly. It applies only when there is a continued threat to public safety and is not an open-ended exception to the Miranda rule,” said Anthony D. Romero, the ACLU executive director.

The Miranda warning would come into play only if prosecutors planned to use any incriminating statements Tsarnaev might make against him. Federal authorities may feel they already have amassed much evidence against the teenager.

Miriam Conrad, the federal defender for Massachusetts, told the Associated Press her office expects to represent Tsarnaev after he is charged. Conrad says she thinks he should have a lawyer appointed as soon as possible because there are “serious issues regarding possible interrogation.”

How to treat the surviving bombing suspect became a matter of debate Saturday in Washington. Four Republican members of Congress demanded that he be treated as an enemy combatant rather than as a common criminal suspect. An enemy combatant can be charged under the laws of war in a military commission or held indefinitely without charge as a prisoner or detainee of war.

In a joint statement, Sens. John McCain (Ariz.), Lindsey O. Graham (S.C.), Kelly Ayotte (N.H.) and Rep. Peter T. King (R-N.Y.) wrote: “The accused perpetrators of these acts were not common criminals attempting to profit from a criminal enterprise, but terrorists trying to injure, maim, and kill innocent Americans.” Tsarnaev, they said, “clearly is a good candidate for enemy combatant status. We do not want this suspect to remain silent.”

Rep. Adam B. Schiff (D-Calif.), a member of the House Intelligence Committee, said the administration “should resist hasty calls to treat the suspect as an enemy combatant. This is not a foreign national caught on an enemy battlefield, but an American citizen arrested on American soil.”

The intelligence community is poring through all terrorism-related intelligence in federal databases, including State Department, Customs and Border Protection, Homeland Security and FBI systems, to see what can be found on Tsarnaev, said an intelligence official who was not authorized to speak on the record.

“What we are doing now is going through basically everything we have, looking for non-obvious terrorist links we might have missed, looking for internal connections, overseas connections,” the official said.

Officials are also interviewing Tsarnaev’s family members in the United States and abroad. The family has roots in Chechnya, a war-torn region in Russia’s Caucasus Mountains. The brothers were raised in nearby Kyrgyzstan before the family moved to the United States in 2002. The younger brother became a naturalized citizen on Sept. 11, 2012.

President Obama posed several questions Friday night in addressing the nation after the bombing suspect was captured: “Why did young men who grew up and studied here as part of our communities and our country resort to such violence? How did they plan and carry out these attacks? And did they receive help?”

Obama added: “One of the things that makes America the greatest nation on Earth, but also, one of the things that makes Boston such a great city, is that we welcome people from all around the world — people of every faith, every ethnicity, from every corner of the globe. So as we continue to learn more about why and how this tragedy happened, let’s make sure that we sustain that spirit.”

The image that is emerging in interviews with those who knew the Tsarnaev brothers is that the older brother, Tamerlan, had become radicalized and troubled in recent years. The FBI revealed Friday that it had questioned Tamerlan in 2011 after being contacted by “a foreign government” — identified by a law enforcement source as Russia — requesting information about him. The agency said it checked government databases and other sources and “did not find any terrorism activity, domestic or foreign.”

Friends of Dzhokhar expressed astonishment about his alleged involvement in the bombings. And Ruslan Tsarni, the uncle of the bombing suspects who previously denounced his nephews as “losers,” moderated his tone in an appearance Saturday on NBC’s “Today” show. Speaking from his Montgomery Village home, Tsarni expressed measured sympathy for Dzhokhar.

“I want him alive,” Tsarni said of his young nephew. “He was used by his older brother. He’s a victim of his older brother. . . . I don’t believe he had full comprehension of what he did.”

Albrecht Ammon, 21, who said he lives on the second floor of the Tsarnaev brothers’ house on Norfolk Street in Cambridge, said he had a recent argument in a pizza parlor with Tamerlan about the Bible and American foreign policy. Ammon said Tamerlan expressed the view that “the Bible is a cheap copy of the Koran” and that the United States goes to war based on the Bible.

Tamerlan also said that “in Afghanistan, most casualties are innocent bystanders killed by American soldiers,” according to Ammon.

The half-hour conversation ended on friendly terms, he said.

“He seemed really smart,” he said of Tamerlan. “It seemed like he didn’t have something against the American people, he had something against the American government, which baffles me with the marathon.”

New details emerged Saturday about the frenzied manhunt that exploded into violence late Thursday night.

The suspects allegedly carjacked a Mercedes-Benz sport-utility vehicle, and the driver escaped at a gas station, leaving behind his cellphone. Police were able to track the Mercedes to Watertown through the abandoned cellphone, said Edward Deveau, the police chief of Watertown, in an interview with CNN.

When a lone police officer confronted the Mercedes, the suspects began firing with multiple guns and threw explosives. More police arrived, and over the course of five to 10 minutes, Deveau said, about 200 rounds were exchanged. At one point, a suspect threw a pressure cooker bomb, like the ones used at the marathon, and it exploded, the police chief said. “We find the pressure cooker embedded in the car down the street, so there’s a major explosion during this gunfight,” he said.

The older brother suffered mortal injuries in the shootout, and late Friday night the bloodied younger brother was discovered by a Watertown resident in his backyard boat just minutes after police announced the lifting of the lockdown.

Saturday, life in Boston began to return to its normal rhythms, though ordinary activities were supercharged by the events of the week. After canceling one game, the Red Sox were back in action at Fenway Park, where a logo on the “Green Monster” left field wall urged the city to “B Strong.”

Players wore special uniforms that said “Boston” on the front instead of “Red Sox,” part of an effort to auction off merchandise that will raise money for a charity to help bombing victims. And Neil Diamond showed up to lead everyone in a rousing rendition of his song “Sweet Caroline,” the Red Sox anthem.

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